Automotive vehicle AM/FM radios are generally configured to receive broadcast radio frequency (RF) signals that are processed at a user selected radio frequency to acquire and play audio content. For example, a listener may select frequency modulated (FM) RF signals in the radio frequency band ranging from about 88.1 to 107.9 MHz, typically selectable at 200 kHz increments. Auxiliary sources of audio content may be available and may be configured to communicate with the vehicle radio to allow for multiple sources of audio content to be played by the vehicle radio.
Conventional methods for injecting an RF signal containing audio content into an existing car radio system 110 generally employ an FM modulator 124 associated with an auxiliary device 122 as shown in FIG. 1. According to one method, the FM modulator 124 outputs an FM modulated RF signal 130 at a predetermined single FM frequency Wc to a switch 120. The switch 120 interrupts the connection from the antenna 118 and its received RF FM signal 132 to the car radio receiver 112 and injects the RF FM signal 130 at predetermined FM frequency Wc. However, this approach generally requires the user to select the appropriate FM station frequency Wc prior to use.
According to another conventional approach, a method detects LO signal leakage from the radio, generally between the radio receiver and the antenna, and determines from the signal leakage which FM frequency station the user is listening to. This method then modulates the audio content at the determined frequency Wc to inject the audio content in an RF signal 130 into the radio by switching the connection from the antenna received RF signal 132 to the RF signal 130 applied to the radio receiver 112 via the switch 120. However, the method of detecting LO signal leakage generally requires sufficient LO signal leakage from the radio to be detected, which typically is not available on many modern day radios. Additionally, this conventional method typically requires the installed radio to have standard RF tuner frequencies.
Accordingly, it is therefore desirable to provide for a system and method of injecting audio content into a radio that does not require user selection of a specific radio frequency or detection of leakage signal from the radio. In particular, it is desirable to provide for a vehicle radio system that allows for an auxiliary audio source to inject audio content into the radio in a manner that is easy to use and reliable.